Editing Universally unique identifier (section)

=== Textual representation ===

In most cases, UUIDs are represented as hexadecimal values. The most used format is the 8-4-4-4-12 format, <code>xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx</code>, where every <code>x</code> represents 4 bits. Other well-known formats are the 8-4-4-4-12 format with braces, <code>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}</code>, like in Microsoft's systems, e.g. Windows, or <code>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx</code>, where all hyphens are removed. In some cases, it is also possible to have <code>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx</code> with the "0x" prefix or the "h" suffix to indicate hexadecimal values. The format with hyphens was introduced with the newer variant system. Before that, the legacy Apollo format used a slightly different format: <code>34dc23469000.0d.00.00.7c.5f.00.00.00</code>. The first part is the time (time_high and time_low combined). The reserved field is skipped. The family field comes directly after the first dot, so in this case <code>0d</code> (13 in decimal) for [[Data Distribution Service|DDS (Data Distribution Service)]]. The remaining parts, each separated with a dot, are the node bytes.

The lowercase form of the hexadecimal values is the generally preferred format. Specifically in some contexts such as those defined in ITU-T Rec. X.667, lowercase is required when the text is generated, but the uppercase version must also be accepted.

A UUID can be represented as a 128 bit integer. For example, the UUID <code>'''550e8400-e29b-41d4-a716-446655440000'''</code> can also be represented as 113059749145936325402354257176981405696. Note that it is possible to have both signed and unsigned values if the first bit of the UUID is set to 1.

A UUID can be represented as a  128 bit [[binary number]]. For example, the UUID <code>'''550e8400-e29b-41d4-a716-446655440000'''</code> can also be represented as 0101010100001110<wbr>1000010000000000<wbr>1110001010011011<wbr>0100000111010100<wbr>1010011100010110<wbr>0100010001100110<wbr>0101010101000100<wbr>0000000000000000<wbr>.

RFC 9562{{r|RFC 9562}} registers the "uuid" namespace. This makes it possible to make URNs out of UUIDs, like <code>'''<nowiki>urn:uuid:550e8400-e29b-41d4-a716-446655440000</nowiki>'''</code>. The normal 8-4-4-4-12 format is used for this. It is also possible to make a OID URN out of UUIDs, like <code>'''<nowiki>urn:oid:2.25.113059749145936325402354257176981405696</nowiki>'''</code>. In that case, the unsigned decimal format is used. The "uuid" URN is recommended over the "oid" URN.